The present invention relates to a compound whose electric, optical or semiconductive characteristics or combined characteristics are modified by introducing an atom C into vacant lattice points of a crystal represented by the general formula AxBy (wherein A is cation and B is anion) while controlling position and/or concentration, concretely, relates to a compound whose dependency of electric resistance ratio to the electric field intensity and the magnetic characteristic are improved by introducing an alkali metal element such as Li or a transition metal element such as Cu which forms a shallow level or a deep level as a dopant into vacant lattice of In2O3 crystal which is Sc2O3 type translational symmetric crystalline lattice structure, or a compound whose electric conductivity ratio is improved by introducing H into vacant point of ZnO which is hexagonal wurtzite type crystalline structure.
In this specification, the term of vacant lattice point does not indicate a random lattice defect observed in a periodical lattice, namely, a lattice defect which means that there is no atom at the point where there is an atom at the ordinary condition, but indicates the group of crystals which has periodic lattice unit including vacant lattice point satisfying the translational symmetricity. That is, the term of vacant lattice point indicates a lattice point which is originally constitute unit cell but absent of atom (vacant) and satisfy the translational symmetricity, to which a introducing atom introduced so as to fill a vacant lattice point and constitute scandium oxide structure periodicity. And in the present invention, the introduction of atom C is called as a vacant lattice filling type introducing.
In general, a crystalline compound represented by a stoichiometric ratio AxBy, for instance In2O3 crystalline compound is an insulator having broad band gap. The technique to improve the electric conductivity of said crystalline compound to the level of metal by introducing an atom which substitute trivalence In and becomes quaternary valence (so called donor type atom) atom such as Sn is proposed.
A thin film of In2O3 has high transmissibility to the visible rays and has a specific feature to reflect the ray of wave length from near infra red to infra red, therefore, based on said specific feature, it is used as a transparent electrode of a liquid crystal display or a thin film solar battery.
However, the endowment of specific feature by said introducing is considered to be caused by Sn4+ which is substituted and solid solved at an In3+ sub lattice point or an oxide vacant hole acts as a donor, however, is not made clear yet theoretically in detail. Therefore, the theoretical clarification for reappearance or stability of it is very difficult. This difficulty is originated from the fact that, for example, the crystalline structure of In2O3 crystal is complicated (a structure as shown in FIG. 9(b), eight octants of (I)-(III) are arranging, and (a) shows a case that three units are arranging), and further originated by the fact that the numbers of atom contained in an unit structure is so many, therefore these atoms are becoming to be related with introducing.
Accordingly, for designing of the substance, the inventors of the present invention have reached to the conclusion that the development of a method to obtain a compound having a desired feature by introducing an atom or ion into crystal structure of a crystalline compound of above mentioned stoichiometric ratio formation with good reproductivity and stability by controlling position and/or concentration is very important. For example, the development of a method to introduce monovalence or divalence ions such as Li+ or Cu2+ into In2O3 crystal is very important.
Therefore, the object of the present invention is to provide a compound prepared by introducing an atom or an ion of said atom into a crystal whose stoichiometric ratio formation is represented by the general formula of AxBy (wherein, A is cation and B is anion) by controlling position and/or concentration. In the other words, the object of the present invention is to develop a method to introduce an atom or an ion of said atom into a crystal whose stoichiometric ratio formation is represented by the general formula of AxBy by controlling position and/or concentration.
The inventors of the present invention, have accomplished the present invention by dissolving the above-mentioned problems. That is, the vacant lattice points can be illustrated as follows. For example, In2O3 possessing Sc2O3 type crystalline lattice structure possesses originally lattice points of 8a, 8b, 16b, 24d and 48e indicated by Wyckoff indication, and among these lattice points, the lattice points occupied by an atom are 8b, 24d (both are In) and 48e (oxygen), while, the lattice points of 8a and 16c are not occupied by atom (vacant lattice point). In the structure of lattice which satisfies stoichiometric ratio formation and translational symmtricity, the lattice point which is not originally occupied by an atom is called as a vacant lattice point. This vacant lattice point is different from the crystal lattice defect characterized as the lack of an atom at the point where an atom exists (this is an introductional subject which can not realize the stoichiometric ratio formation). By establishing a method to introduce an atom to said vacant lattice point, the present invention is accomplished. For example, the compound which has desired characteristics can be designed by introducing a typical metal element Li or a transition metal element Cu to In2O3 crystal so as to provide varistor characteristic or magnetic characteristic based on a transition metal or by selection an atom to be introduced. Further, the example to improve the electron conductivity by introducing hydrogen atom to the vacant lattice point of ZnO can be mentioned. When an atom having radius r is introduced to the vacant lattice point of various crystalline compounds represented by the general formula AxBy and forms a close-packed structure, the maximum radius of an octahedral hole or a tetrahedral hole becomes respectively 0.4 r and 0.2 r. An atom species which provides desired electronic characreristic should have atom radius within the limit restricted by geometrical condition of crystalline structure of the subjected compound. That is, when the varistor characteristic is desired, s electrons having ionic bond feature should be selected, while, when the excellent electron conductivity is desired, d electrons having covalent bond feature should be selected. The atom which can provide the desired characteristic to the various mother crystal by being introduced into the vacant lattice point of said mother crystal is selected previously, namely, the energy band electron structure when the atom is filled into vacant lattice point of the mother crystal is calculated. And the compound having desired feature which will be obtained by the actual introducing based on said calculation is designed and prepared. For the calculation of energy band electronic structure, technical skills such as the first-principle band calculation, the fight bonding approximation band calculation method or the cluster electronic structure calculation method are used at need.
The idea of this invention which obtain a compound having desired characteristic by introducing an expected atom to a vacant lattice point (vacant lattice point designed so as to generate novel characteristic) of the crystalline compound represented by above mentioned general formula is a quite new idea.
Therefore, as mentioned above, for the purpose to distinguish from the conventional substitutional type, the dopant introducing method of the present invention is named as an introducing type.
The present invention is a compound whose dependency of electric resistibility to the electric field intensity and the magnetic characteristic are improved by introducing an alkali metal element such as Li or an transition metal element such as Cu which forms a shallow level or a deep level as a dopant into vacant lattice of In2O3 crystal which is Sc2O3 type translational symmetric crystalline lattice, or a compound whose electric conductivity is improved by introducing H into vacant point of ZnO which is hexagonal wurtzite type crystalline structure.